Screw thread grinding machine



April 20, 1943. I. J. SNADER SCREW THREAD GRINDING MACHINE Filed Oct. 30,1940 1l-Sh eets-Sheet 1 April 20, 1943. J. SNAD ER SCREW THREAD GRINDING MACHINE l1 Sheets-Sheet 2 MGN Filed Oct. 50. 1940 v mi/Il NVEN'FOL/ r'a CfaSno o er f, 4 I M $3, a MI I (flT-rocmgzs April 20, 1943.

l. J. SNADER SCREW THREAD GRINDING MACHINE Filed Oct. 50. 1940 ll Sheets-Sheet 5 NVEL-NTOL/ ra (ZS/adder fi 1943- 1. J. SNADER 2,316,816

' scaaw THREAD GRINDING MACHINE Filed Oct. 30, 1940 11 Sheets-Sheet 4 mu 3 7; (f7 Shae er April 2), 1943. I. J. sNADER 2,313,816

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l. J. SNADER SCREW THREAD GRINDING MACHINE Filed Oct. 30, 1940 11 Sheets-Sheet 7 r62 Cf cS/vaa e April 1943' l'. J. SNADER I 2,316,816

SCREW THREAD GRINDING MACHINE Y Filed Oct. 50, 1940 ll'Sheets-Sheet 9 Q R CPI wycaw'romd Q 7 Tra CZ 6170619 1% W 4; 614%; r W

TTOwys April 20, 1943. l. J. SNADER 2,316,816

SCREW THREAD GRINDING MACHINE Filed Oct. 30,1940 ll Sheets-Sheet l0 TTO may;

Patentecl Apr. 20, 1943 SCREW THREAD GRINDING MACHINE Ira J. Snader, Detroit, Mich, assignor to Ex- Cell-O Corporation, Detroit, Mich., a corporation of Michigan Application October 30, 1940, Serial No. 363,445

21 Claims.

The invention relates to thread grinding machines generally and more particularly to an improved machine for grinding internal screw threads.

One object of the invention is to provide a precision thread grinding machine of the above general character which is especially suitable for operation under high production conditions and which is readily adjustable for grinding either straight or tapered threads in a wide variety of different sizes and thread forms.

Another object is to provide an improved internal screw thread grinding machine embodying novel means for controlling relative feed of the work and grinding wheel to insure a high degree of accuracy in the finished product.

Another object is to provide novel means for supporting the work so that it may be suitably presented to the grinding wheel yet readily accessible for loading and gauging.

Still another object is to provide novel lead screw adjusting means for accurately matching the grinding wheel to preformed threads of the work piece and for effectually neutralizing any back lash in the lead screw drive and associated parts.

A further object is to provide novel means for coordinating a dressing device with an adjustable grinding wheel so as to dress the wheel to the correct shape for the particular work it is set to perform and to maintain a predetermined relationship between the tool and work at all times.

Another object is to provide novel means for tensioning the driving belts, chains, etc., by which the various machine elements are driven.

Other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment illustrated in the accompanying drawingsin which:

Figure 1 is a perspective view of an internal screw thread grinding machine embodying the features of the invention.

Fig. 2 is a skeleton perspective view of the machine showing the relationship of the operating and adjusting elements.

Fig. 3 is a transverse vertical sectional view through the grinding wheel supporting structure taken along the line 3-3 of Fig. 1.

Fig. 4 is a vertical sectional view taken along the line 44 of Fig. 3 showing details of the grinding wheel support.

Fig. 5 is a vertical sectional view through the wheel supporting structure taken along the line 55 of Fig. 1.

Fig. 6 is a sectional view taken on a vertical plane through the axis of the main feed shaft substantially along the line 6-6 of Fig. 3.

Fig. 7 is a vertical sectional view taken alon the line l--l of Fig. 5 showing details of the mechanism for driving .the main feed shaft.

Fig. 8 is a transverse sectional View of the work supporting head and the driving and actuating mechanisms for the same taken along the line 8-8 of Fig. 7, the head being shown in loading or gauging position.

Fig. 9 is a sectional view of the work supporting head taken on a plane through the axes of the work supporting spindle and the main feed shaft substantially along the line 9-9 of Fig. 8.

Fig. 10 is a transverse sectional view of the work supporting head and associated apparatus taken along the line Ill-4'0 of Fig. 9 showing the head in grinding position.

Fig. 10 is a fragmentary perspective view showing details of the reversing mechanism.

Fig. 11 is a fragmentary sectional view of the master feed screw and nut assembly taken along the line |I-ll of Fig. 6.

Fig. 12 is a fragmentary sectional view of the work head positioner taken in a vertical plane substantially along line I2-l2 of Fig. 9.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail, the preferred embodiment, but it is to be understood that I do not thereby intend to limit the invention to the particular form disclosed but intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

The machine selected to illustrate the invention comprises generally an elongated horizontally disposed base 20 having at one end a grinding wheel supporting structure 2| (Figs. 1-4) and at the other end a translatable work carriage 22 (Figs. 1 and 6-10). In this machine a grinding wheel 23 is rotated in a relatively fixed position while a work piece W (Fig. 2) is rotated and fed axially across the plane of the wheel at a rate determined by the lead or pitch of the threads to be ground thereon. The grinding wheel 23 is suitably supported on a housing or head 24 swiveled to the wheel supporting structure so. that it may be accurately alined with the helix angle of any thread within the range of the machine.

To regulate the depth of out taken by the grinding wheel, rough adjustments are made by shifting the wheel head transversely of the work while fine adjustments are effected by a lateral shifting of the work. To this end the work is supported on a head 25 swiveled to the work carriage for pivotal movement about an axis parallel to the reciprocatory path of the carriage. This mounting of the head is further advantageous in permitting the head to be swung toward the front of the machine into a conveniently accessible pofixed to the rear wall of the sition for loading or gauging the work. For grinding taper threads the entire wheel supporting structure 2| is shifted transversely of the base in timed relation to the feed of the work.

The wheel supporting structure is additionally arranged to carry a suitable wheel dresser or truing device. The device ispreferably located intermediate the wheel head and work head and positioned to engage the wheel on the same side that the wheel engages the work. With'this arrangement the dresser acts as a sizing device and materially facilitates the maintenance of the correct relationship between the grinding wheel and work regardless 'of the number of dressing operations or the variations of the diameter of the wheel due to successive dressings,

Referring more particularly to Figs. 2-5 of the drawings the wheel supporting structure 2| comprises a primary slide 3|, hereinafter called the taper slide, having on its upper face a dovetailed slideway 32 for a secondary slide 33, conveniently called the wheel slide, and spaced parallel V-ways' 34 for a dresser slide 35 (Fig. The taper slide as herein shown is in the form of a flat, generally rectangular table supported for movement transversely of the machine base by rollers 36 (Figs. 2 and 4) operating on parallel horizontal fiat ways 31 and inverted V-ways 38 formed on the upper part of the base.

Projecting fromlthe front end of the taper slide and out through the front wall of the machine base are a pair of hollow generally cylindrical stems 4| and 42 alined respectively with the ways for the wheel. slide and the dresser slide. These stems carry the manualcontrois for adlusting the position of the slides as will be described in detail'hereinafter.

The taper slide 3| and apparatus carried thereby is urged rearwardly by a coiled compression spring 45 interposed between a thrust plate 48 slide and a thrust block 41 bolted or otherwise rigidly secured to the machine base. A guide rod 48 secured at one end to the plate 46 and slidable in an aperture in the block 41 extends through the spring to maintain it in place.

Movements of the taper slide under the action of the spring are controlled by a cam bar 50 coacting with a follower roller 5| on the slide. The cam bar, in this instance, is affixed at one end to a push bar 52 operatively secured to the work carriage 22 as will appear presently, so that the 'cam bar follows the work in its feed movements relative to the grinding wheel. As herein shown, the roller is Journaled on a vertical pin 53 fixed to the stem 4|, the stem being notched as at 54 for the reception of the roller and the bar.

Itwill be apparent from the foregoing that the position of the taper slide at any instant in the operating cycle will depend of the front edge of the bar 50 against which the follower roller is urged by the spring 45. Thus by providing a cam bar appropriately shaped in accordance with the taper of the work piece to be ground, as indicated by the broken line 55 in Fig. 2, the slide and grinding wheel carried thereby will be caused to automatically follow the proper course as the work is fed to the wheel. Conversely, straight work may be upon the form.

ground by providing a straight cam bar which will operate to maintain the taper slide in fixed position throughout the grinding operation. To facilitate interchange, the cam bars are arranged to be disengageably secured to the push bar 52 as by an interfltting lug and notch connection 55 The wheel slide 33 as herein shown comprises a generally rectangular table dovetailed t0 the slideway 32 on the taper slide so that in addition to moving with the taper slide it is also capable of moving relative thereto but in a path parallel to the path of the latter slide. Adjacent its front end the wheel slide is provided with an upstanding bracket 6| for supporting the wheel head 24. This head is preferably a rigid metal casting having two vertically and laterally offset parallel cylindrical portions 62 and 63 connected by webs 64 with a vertical back portion 65. The cylindrical portions are slotted longitudinally to form split friction clamping sleeves for a grinding wheel assembly 66 and an idler pulley supporting stud 61, respectively. Bolts 63 threaded into flanges into opposite sides of the slots-serve to draw thesleeves into clamping position.

The wheel assembly 66 may be of any suitable and well known type such as a highspeed grinding spindle of which various kinds are in general use. As herein shown, the assembly comprises a cylindrical shell 1| in which is journaled a spindle 12 having at one end an interchangeable quill 13 carrying the grinding wheel 23. The shell is adapted to fit into the sleeve 62 and is rigidly clamped therein by tightening the bolts 68. The rear end of the spindle is equipped with a multiple V-groove driving pulley 14.

In the present instance the spindle 12 is driven from an idler pulley 15 by a series of V-belts II, the idler pulley being driven by a motor M through a pair of V-belts 16'. The'idler pulley is journaled on an eccentric shaft 1 I projecting from one end of the stud which is frictionally clamped in the split sleeve 63. Due to theeccentric location of the shaft 11, the drivingbelts can be suitably tensioned by simply rocking the stud about its longitudinal axis before clamping it in the sleeve. Moreover, the idler pulley and its support can be shifted axially to maintain correct alinement with the spindlepulley 14 in the various adjusted positions of the wheel assembly 5'.

In grinding threads,'the grinding wheel must.

of course, be alined with the helix angle of the threads. To provide for such alinement the grinding head is supported on a swivel mounting which allows the head to pivot in a vertical plane about a reference point P marking the intersection of the wheel axis with a horizontal line passing throughthe point at which the wheel engages ence to Fig. 4, the plate is provided on its front.

face with a pair of arcuate T-s'lots 82 formed on radii centered at the point P. T-bolts 83 passing through the back portion 55 of the head and engaging in the slots serve to guide the head in its pivotal movement and to lock the same in any set position.

For adjusting the position of the head, an adjusting screw 84. is rotatably anchored in a vertical slot 85 in the plate 8|, the top 86 of the screw being appropriately shaped for engagement ment with the nut 81.

by a suitable wrench. Disposed in the slot 85 and cooperating with the adjusting screw is a nut 81 having a forwardly projecting cylindrical boss 88 fitting in a socket in a generally rectangular slide block 89 seated in a transverse slot 90 in the back portion 85 of the head. The arrangement is such that vertical movements of the nut 31 resulting from the rotation of the adjusting screw are effective to shift the head along the slots 82 which guide the head in an arcuate path centered at the point P. In this adjustment the block 88 swivels with respect to the boss 88 and moreover. it slides along the slot 90 to maintain it in aline- To facilitate adjustment of the head a graduated plate 9I is fixed to the face of the mounting plate 8I to cooperate with a pointer 92 carried by the head.

The motor M which drives the grinding wheel spindle is desirably carried on the wheel slide 33 adjusted positions of the wheel head and the wheel assembly, the motor is mounted on a cradle 93 dovetailed to an arcuate slideway 94 fixed to the wheel slide. The motor may thus be tilted by rocking the cradle on its slideway to conform to the alinement of the wheel head as above explained. Moreover, the motor is secured to the cradle by means of a T-bolt 95 engaging T-slots 96 extending longitudinally of the cradle so that it may be shifted to the left or right to conform to any set position of the idler pulley. As shown in Fig. 1, the belts and pulleys are enclosed by suitable guards 91. I

The wheel slide 33 is adapted to be shifted along its guideway by means of a feed screw I00 actuated by suitable manual controls accessible at the front of the machine to set the grinding wheel in a predetermined position of adjustment with respect to the work and dressing device.

of the hand wheel and parts associated therewith. To facilitate accurate adjustment of the slide an adjustable pointer II! is provided on the hand wheel for cooperation with the suitable indicia on the gear housing. As herein shown the pointer is secured to the hand wheel by means of a T-bolt II8 operating in an arcuate T-slot H3 in the face of the wheel.

The dresser slide is located between the wheel slide 33 and the work head 24 and is supported for reciprocation in a path generally parallel to the reciprocatory path of the wheel slide. The support is provided in this instance by roller bearings I2I operating on the V-ways 34 which are formed on opposite side edges of a fiat generally rectangular plate I22 bolted or otherwise rigidly secured to the, face of the taper slide 3|.

A dowel pin I23 serves to locate the-plateaccurately with respect to the wheel slide. The dresser slide itself comprises a flat generally rectangular tablehaving secured to its upper face a pair of spaced keys I24 for accurately locating a wheel dresser or truing device on the slide. The dresser (not shown) may be of any suitable character,

As shown in Fig. 3, the feed screw projects forwardly through the hollow stem M of the taper slide and is supported at its inner end in a thrust block IOI which is disposed in a recess in the face of the taper slide and bolted or otherwise rigidly secured thereto. The feed screw is held against endwise movement by means of thrust sleeves I02 and I03 carried on the reduced end portion of the shaft and respectively engaging roller thrust bearings I 04 and, I05 fixed in the thrust block I0 I. Forwardly of the sleeve I02 the feed screw is threaded for engagement with a feed nut I06 keyed in a recess in a block I01 bolted or otherwise rigidly secured to the underside of the wheel slide 33. Thus, rotation of the feed screw acts through the nut to impart forward and reverse movements to the slide. I

f The outer end of the feed screw I00 projects from the stem 4| into a housing I08 and has fixed thereto a gear I09 meshing with a pinion IIO on a stub shaft III journaled in the housing. The outer end of the shaft III is keyed to a hand wheel II2 which may be rotated by a handle II3 to drive the feed screw and thus shift the slide on its guideway. The slide may be locked in adjusted position by means of a thumb screw II4 threaded into the hand Wheel'and having its inner end tapered for engagement with the similarly tapered end of a radially disposed locking pin II5 slidably supported in a boss on the inner side of the hand wheel. The boss projects into a cylindrical recess H6 in the housing I08 and the thumb screw acts to force the locking pin outwardly into frictional engagement with the peripheral wall of the recess to prevent rotation machine.

for example, a universal dresser of the general type disclosed and claimed in my copending application Serial No. 350,362, filed August 3, 1940.

In the exemplary machine the dresser slide is normally held in a retracted or inactive position while the grinding wheel is operatingon the work and is shifted forwardly to a predetermined position of adjustment with respect to the work to dress the wheel. This dressing operation is performed at the point at which the wheel engages the work thus enabling the dresser to function as a sizing device for accurately determining the depth of cut taken by the wheel.

While any suitable means may be utilized for shifting the dresser slide between its operated and inactive positions, it is preferred toemploy pressurefiuid actuated means for this purpose. The actuating means asherein shown comprises an air cylinder I25 rigidly mounted'at its rear end on a bracket I26 fast on the taper slide. The cylinder is provided with a suitable double acting piston having its forwardly projecting piston rod I21 anchored to a thrust block I28 bolted to the dresser slide. Air under pressure is admitted to opposite ends of the cylinder selectively by suitable controls including a manual lever I29 (Fig. 1) located at the front of the These controls are interlocked with the controls for actuating the work head so as to effectually prevent interference between the elements as will appear presently.

Since the tool dresser acts as a sizing device and determines the point at which the grinding wheel engages the work, it is essential to locate its operated position with a high degree of accuracy. This is accomplished in the present instance by a stop member I3I (Fig. 5) positioned below the dresser slide for engagement by a stop block I32 rigidly secured to the underside of the slide. The stop member I3I is in the form of a generally rectangular block having arecess in its upper surface defining a shoulder or abutment I33 disposed in the path of the stop block I32. The stop member is slidably confined at its upper end ina slot I34 extending longitudinally of the V-plate 122 with its lower end portion projecting into a recess in the face of the taper slide. Keyed in the lower-portion of the stop member is a nut I35 coacting with a feed screw I36 which extends forwardly through the stem 42 into a gear housing I31 mounted on the 7 herein shown as integrally formed on a stub shaft I43. The latter shaft is suitably journaled in the housing I31 and to its outer end is keyed a hand wheel I adapted to be turned by a handle I45. Through this arrangement the feed screw may be rotated to shift the stop l3| to any desired setor adjusted position in which it ac- "curately locates the forward limit position to which'thedresser slide may be shifted by the actuating means. The stop may then be locked in set position by means of a thumb screw I45 on the hand wheel acting to shift a radially disposed locking pin "I41 into frictional engagement with the peripheral wall of a cylindrical recess 5 in the gear housing. A suitable scale I on the housing "adjacent the wheel facilitates accurate setting of the stop.

After the grinding wheel and dresser have been adjusted or set in the manner above described. the work piece W is advanced into engagement with the grinding wheel by a feed movement of the work carriage 22 on which the work head is swiveled as mentioned hereinbefore. The work carriage as herein shown comprises a pair of axially alined slides I5I (Figs.,2, 6 and 8-10) and I52 (Figs. 2, '7 and 9) hereinafter referred to respectively, asthe right hand and left hand slides. Both slides are supported on a common horizontal guideway' extending longitudinally of the machine base or perpendicular to the guideway for the taper slide previously described. The guideway in this instance is formed by V-shaped grooves in the opposed faces of spaced parallel guide bars I55 bolted or otherwise rigidly secured to the top of the machine base. Roller bearings i5| are interposed between the slides and the ways to reduce friction.

The action of the cam bar in controlling the position of the taper slide 3| in the movements of the work carriage has previously been described. Movements of the carriage are imparted to the cam bar by the push bar 52 which, as shown in Figs. 2 and 9, is adjustably connected to the left hand slide I52 by a retainer plate I55 removably fixed to the slide and engaging in spaced notches I55 in the upper face of the bar. The bar, incidentally, is slidably supported in a longitudinal channel in the machine base which is closed by an elongated cover member I55 (Fig. 3).

The slides I51 and I52 support the work head 25 which preferably comprises an elongated hollow casing portion I56 having depending legs I51 and I58 at opposite ends for pivotal connection with the respective slides. For connecting the head with the slide I5I the le I51 is-apertured to receive one end of the hollow cylindrical plug I59 (Fig. 61 which is rigidly secured to the leg by bolts passing through a peripheral flange I55 on the plug. The other end of the plug is journaled in bushings I61 carried in a hollow cylindrical sleeve member l52f0rmed integrally with the slide I5I.

The other leg I58 of the head structure is i'ournaled on a shaft I63 supported in a pair of cylindrical members I64 and I85formed on the left hand slide I52. ihe'members being spaced aeiaaie apart as shown in Figs. 2 and 9 for the reception of the leg. A locking screw I68 threaded into the member I55 holds the shaft in place. Both of the above members are arranged on a commcn axis with the sleeve member I52 of the right hand slide which axis is parallel to the guideway for the slides. The work head is accordingly adapted to rock transversely of the reciprocating path of the work carriage between a rearward or operating position and a forward loading or gauging position as will be described in more detail hereinafter.

The work piece to be operated upon by the grinding wheel is supported on the head by a suitable chuck (not shown) bolted or otherwise rigidly secured to the nose of a hollow spindle I10 (Figs. 6 and 9) supported on antifriction bearings MI in the hollow casing portion I56 of.

the head. The spindle is disposed with its longi-t tudinal axis parallel to the axis of the guideway for the work carriage so that in the feed movements of the carriage the work supported by? the spindle is fed in an axial direction across the plane of the grinding wheel.

Coolant is supplied to the work'during the grinding operation through a hollow tube I12 anchored at one end in a cap I13 bolted to the casing at the rear of the spindle, the tub .extending through the spindle substantially to the nose portion thereof. Coolant supplied from any suitable source is delivered to the tube through a pipe I14 and valve I15 which is threaded into the cap in communication with the tube. A packing gland or gasket I15" interposed between the end of the spindle and the adjacent face of the cap excludes coolant from the interior of the casing and thus protects the spindle bearings. To prevent objectionable splashing of the coolant, a generally cylindrical guard I15 is secured to the head to enclose the outer end of the spindle and to extend over the work piece.

In grinding screw threads, the work must be 7 rotated in timed relation to its axial feed as determined by the pitch of the threads being ground. Exact coordination of rotation and feed is obtained in the present instance by utilizing a common power actuated member or feed shaft I11 (Figs. 2 and 5-9) for driving the work spindle and for imparting feed movements to the car: riage. The feed shaft is arranged axially of the head supporting plug I59, that is, coaxial with the pivot for the work head and is rotatably sups ported by an antifriction bearing I18 seated in the plug receiving recess in the leg I51. The inner race ring of the bearing is confined between a shoulder I19 on the shaft and the hub of a gear I80 fast on .the shaft while the outer race ring of the bearing is confined between the end of the plug I59 and a coverplate l8I bolted to the leg I51 to prevent endwise movement of the shaftrelative to the work head in either direction. I

The gear lali 'is utilized to drive the work spindle either forwardly or reversely forggrinding right orleft hand threads. For this 'p'iirpose a pair of intermeshing gears I82 and I83 (Figs. 2 6

and 8) are rotatably mounted on a shiftable'lg bracket I84 which is supported on a cylindrical extension IIl5-of the cover plate I8I to pivot about the axis of the feed shaft. The-gear I82, conments to the work carriage holds the latter gear against endwise movements relative to the spindle.

The gear I83 is an idler gear permanently meshing with the driving gear I82 and adapted when the bracket I84 is swung to its alternate position to mesh with the spindle gear I86. In this alternate position of the bracket, the drive gear is disengaged from the spindle gear so that the spindle is driven reversely through the idler gear. For shifting the bracket, a short adjusting shaft I88 journaled in the leg portion I51 of the head is provided at one end with an eccentrically disposed pin I89 engaging in a slot I89 in the bracket. The other end is conveniently accessible at the front of the head for turning by means of a wrench or other suitable tool.

The feed shaft I11 acts to impart feed movethrough the medium of a master lead screw and nut assembly I90 (Figs. 6 and 11) which is readily interchangeable for grinding threads of different pitch. The assembly as herein shown comprises a lead screw member I9I in the form of an elongated sleeve having accurately formed threads corresponding in pitch to the pitch of the threads to be ground. The screw member is adapted to fit over the reduced outer end portion of the feed shaft and is nonrotatably secured thereto as by a key I92. Annular spacers I93 interposed between the inner end of the member and a shoulder I94 on the shaft and between the outer end of the member and a stop washer I95 removably fixed to the end of the shaft serve to accurately position the member on the shaft and to hold it against endwise movement relative thereto. The spacers are interchangeable so that the position of the lead screw may be varied as required for different types of work. Moreover, lead screws of different length may be employed thus making it unnecessary to utilize long relatively expensive lead screws for relatively short work pieces.

Cooperating with the lead screw I9I is a relatively stationary master lead screw nut I96 which is removably secured within a hollow, generally cylindrical supporting member I91 as by. dowel screws I98. While the nut remains stationary during the operation of the machine, it is at times desirable to rotate it to advance the work carriage for accurately matching preformed threads in a work piece with the grinding wheel. To this end the supporting member is rotatably mounted in a housing I99 rigidly supported on the machine base 20. A worm wheel 200 (Fig. 11) fixed to one end of the member is arranged to be driven by a worm i carried on a cross shaft 202 journaled in the housing. A hand wheel 203 keyed to the outer end of the shaft provides convenient means for rotating the shaft.

Means is also provided for imparting incremental rotational steps of predetermined length to the feed nut supporting member to take up any back lash in the feed mechanism which may develop as the parts become worn from extensive use. This means as herein shown comprises a wheel 204 rotatably mounted on the hub of the hand wheel 203 and adapted to be locked thereto by a radially disposed pin 205 shiftable axially by a thumb screw 205 on the hand wheel into frictional engagement with a peripheral wall 201 of a recess in the wheel 204. A hand lover 208 is fixed to the wheel 204 in radially projecting relation for convenient manual operation.

In order to confine the movements of the nut within predetermined limits required to compensate for the back lash present at any given time,

with a dovetailed the wheel 204 is formed on its peripheral edge way 209 on which are mounted a pair of adjustable dogs 2I0 adapted to cooperate with a stop 2II rigid with the housing I99. These dogs may be locked in place on opposite sides of the stop and spaced apart circumferentially of the wheel so that the permitted angular movement of the wheel is just sufficient to take up the back lash.

In the exemplary machine the feed shaft and associated parts are effectually protected from the entry of dirt or other foreign matter by shields of sheet metal or the diate portion of the feed shaft, the right hand slide I5I and the ways therefor are covered by a telescoping housing which automatically adjusts its length in accordance with the feed movements of the work carriage. The housing as shown in Fig. 6 comprises an outer guard member 2 I2 fixed to the work head and telescoping over an inner guard member 2 I3 fixed to the feed nut housing. A gasket 2I4 of felt or other suitable material provides a tight joint between the members yet permits the relative movement necessitated by the feed and return movements of the work head. The outer end of the feed shaft is enclosed by a tubular cap 2I5 carried on a cover plate 2IIi closing the end of the feed nut housing. The cover plate is secured to the housing in a manner permitting convenient removal to give access to the feed screw and nut assembly for replacement of the same.

Suitable power actuated means is provided for driving the feed shaft I11 in either direction to advance or retract the work carriage relative to the grinding wheel. In the exemplary machine, the drive for the feed shaft includes a splined drive shaft 22I (Figs. 2, '1 and 8) disposed in the machine base below and substantially parallel to the feed shaft. A flexible'driving element 222 such as a belt or chain drivingly connects the two shafts. The driving element illustrated is in the form of an endless belt oper- 'ating on one pulley or sprocket wheel 223- fast on the inner end of the feed shaft and a second pulley or sprocket wheel 224 splined on the drive shaft. Due to the splined connection, the sprocket wheel 224 is capable of being shifted axially of the shaft to maintain alinement with the sprocket wheel 223 as the latter reciprocates with the work carriage. Shifting of the sprocket wheel 224 along the drive shaft is effected in the present instance by means of a depending arm 225 rigidly secured at its upper end to the left hand slide I52 of the work carriage and having at its lower end a shoe 226 confined between a pair of spaced thrust rings 221 rigidly secured at opposite ends of the sprocket wheel.

To permit adjustment of the tension of the driving element or chain which may become necessary from time to time through wear in extended use, the drive shaft is journaled at opposite ends in eccentric supporting members or bushings 228 and 229. At its .left end (as viewed in Fig.7) the shaft is carried on an antifriction bearing 230 mounted on a hub portion 23I of a housing 232 (Fig. '1),which is mounted eccentrically in the bushing 228. At its opposite end the shaft ,is supported by an antifriction bearing233 eccentrically disposed in the bushing 229. The bushings, in turn, are rotatably supported in bearing plates 234 and 235 carried on the machine base 20, the first mentioned bearing plate being formed with a flangelike extension 236 extending upwardly along the like. The intermeend wall of the base. Due to the eccentric location of the shaft with respect to the bearing surfaces of the bushings, rotation of the latter will operate to oscillate the shaft bodily and thus vary its distance from the feed shaft. Rotation of the housing 232 with its associated bushing. is prevented by a headed pin 231 set in the bearing plate 234 and slidably engaging in a slot 238 in back of the housing.

Rotation of the bushings 228 and 229 is effected simultaneously by meansof an adjusting shaft 239 journaled in the machine base above but parallel to the drive shaft. Gears 248 and 24| pinned to the adjusting shaft mesh respectively with gears 242 and 243 fixed to the respective bushings. A hand lever 244 engaged on the squared edge of the adjusting shaft is provided for rotating the same. At its outer end the lever carries a pin 245 which can be entered in any one of a series of arcuately arranged holes 246 in the bearing plate extension 236 to retain the adjusting shaft in set position.

For driving the shaft 22!, the left end thereof (as viewed in Fig. 7) is extended into the housing 232 and haskeyed thereto a worm Wheel 2511 meshing with a worm 25i carried by a cross shaft 252 journaled in the housing. The cross shaft is driven by a motor Ml (Fig. 2). by a V-belt 253 and grooved pulley 254 which is keyed to the inner end of the shaft.

7 The motor Ml is of the reversible type and is adapted to be controlled manually by push button switches located on a switch panel SP (Fig. 1) at the front of the machine or automaticallyby a reversing switch RS (Fig. 10) actuated by the work head as will appear presently. To prevent the pull I on the driving belt from rocking the housing structure and thus changing the tension of the driving chain, the housing is securely locked in set position by a locking bolt 256 rigidly anchored in the bearing extension 236 and projecting through a slot 251 in the housing.

.The drive shaft 22| may be utilized conveniently for-driving a lubricating pump 258v (Fig. 7) shown diagrammatically in Fig. 7 as mounted on the right hand end wall of the machine base 28. Since the drive shaft is mounted to oscillate for chain adjustment, the drive for the pump is desirably taken through an intermediateshaft assembly including a pair of universal joints 259 connected by a driving link 260.

Before initiating the feed of the work carriage, the work head must be swung from the inactive or loading position shown in Fig. 8 to the operating position shown in Fig. 10 in which the work is alined in operative relation with the grinding wheel 23. While the head can be swung manually between these two positions, it is preferred to employ power actuated means for this purpose. The power actuated means in its preferred form comprises a pressure fluid motor herein shown as an air .cylinder 26I mounted on a rigid frame 262 secured to the machine base at the rear of the head'as shown in Fig. 10. The cylinder is fitted with a double act ing piston 263 having a forwardly extending piston rod 264 operatively connected with a reciprocatory member or cross head 265 slidably supported in a guideway on the frame 262 for movementin a path perpendicular to the pivotal axis of the work head.

Movements of the cross head are communicated to the work head through a toggle mechanism including a bell crank lever 268 pivoted on a horizontal shaft 26! carried on the frame 262.

- rearwardly and upwardly from the casing por-.

mechanism .288 (Figs. 8,

apertured at its other end to slidably receive a shaft 210 held between spaced pillow blocks 21! secured to the rear face of the work head.

The sliding connection between the link and the shaft permits the actuating means to be stationarily supported on the base, instead of reciprocating with the head and thus materially simplifies the machine structure. A spring 212 interposed between the adjacent ends of the cylinder 26l and cross head 265 counterbalances the weight of the head.

Air under pressure may be admitted to either end of the cylinder 26l selectively by means of suitable controls including a manually operable hand lever 213 conveniently-accessible at the front of the machine. When air is admittedto the outer end of the cylinder, the piston and.

cross head are shifted forwardly thus rocking the head to the position shown in Fig. 8 in which the work spindle is readily accessible at the.

front of the machine for loading the work piece thereon or for gauging a work piece carried by the spindle. The admission of air to the inner end of the cylinder shifts the cross head rearwardly to break the toggle and swing the head to the operating position shown in Fig. 10. a

The controls for the work head actuating mechanism are effectually interlocked to prevent actuation of the same to loading position when the work carriage is in an advancedposition. 'For-this purpose a suitable control valve V(Fig. 2) is interposed in the air line leading to the cylinder 26l. A dog.2|4 (Figs. 2 and 8) adiustably mounted in a T-slotted bar 215 fixed V to the left hand work carriage slide IE2 is arranged to actuate the valve and block the admission of air to the cylinder at all times except when the work carriage is in its fully retracted position. 7

Since the operating position of the work head determines the lateral relationship of the work and grinding wheel and therefore the depth to which the grinding wheel will cut into the work,

it is essential that this position be locatedwith a high degree of accuracy. Thisis accomplished in the present instanceby a novel positioning 10 and 12) which is adjustable for varying the operating position in incremental steps so that fine adjustments for depth of cut can be quickly and accurately made.

The positioning mechanism as shown in Fig. 12

comprises a hardened cylindrical stop button 28! threaded into one end of an elongated stop shaft 282 threading into a flanged nut 284 seated in .a recess in a boss 285 projecting against .endwise movement. Rotation of the nut is prevented by a pin 28'! engaging in a slot'or aperture in the flange of the nut.

Rigidly secured on suitablelocating pads 288- which has. an enlarged cylindrical body portion 283 on the frame 262 as by clamping members 289 is a fixed stop in the form of a horizontal positioner bar 298 disposed in thepath described by the stop button in the rocking movements of the work head. The positioner bar extends parallel to the reciprocatory path of the head and is of wear on the parts.

sumcient length to engage the stop button in any position of the work carriage along its guideway. The engagement of the stop button with the positioner bar, of course, limits the 7 range of movement of the work head and thus determines the relative lateral position of. the work with respect to the grinding wheel.

Fine adjustments in the position of the work are made by screwing the stop shaft 282 into or out of its associated nut. For this purpose the upper end of the shaft is extended through the cover plate 283 and to the projecting end is keyed a radially projecting handle 29! con veniently accessible from the front of the machine. The handle is, formed with a depending shoulder portion 292 facing the peripheral wall of a cylindrical projection 293 on the plate 238. A hardened locking pin 29l.'siidably disposed in a passage extending from the shouldered portion of the handle and back through the outer end thereof is adapted to be shifted forwardly into frictional engagement with the projection 293 by rotation of a tubular gripping member 294 mounted on the end of the handle to lock the handle in set position. For this P p se a rod 295 is disposed axially within the gripping member and non-rotatably anchored thereto. This rod is threaded into the outer end of the passage for the pin 294. rod resulting from the rotation of the gripping member are transmitted to the locking pin by an intermediate pin 296.

To facilitate adjustment of the work head and insure accurate finishing of the Work exactly to the desired dimension, a stop 29'! is provided for limiting the range of movement of the handle 29]. The stop as herein shown is adjustably secured in a T-slot 298 in the cover plate 286 and is arranged to project into the pathvof the shoulder portion 292 or the handle. At the beginning of an operating cycle, the handle may be swung around to retract the stop shaft and thus permit the head to swing through a maximum stroke. In this position of the head the grind ng wheel will take arelatively shallow cut. The depth of cut may then be increased progressively by shifting the handle through a series of small steps after each pass of the work relative to the grinding wheel until the limitposition defined by the stop 291 is reached.

Means is desirably provided for cushioning the shock incident to the engagement of the positioner bar by the stop button so as to reduce The cushioning means as herein shown comprises a dash pot mechanism incorporated in the stop shaft 282. Referring to Fig. 12, the stop shaft is formed with a cylindrical, axially alined recess 300 in which a plunger 3'. is slidably disposed. .A hollow stem 302 projects from the lower end of the plunger through a suitable passage in the stop button.

An annular packing ring 303 of leather or other suitable material is clamped to the inner end of the plunger by means of a headed bolt 304 threading into the hollow stem. The packing ring provides a sealing fit with the walls of the recess 300 thus enabling the plunger to compress the air entrapped in the inner end of the recess. 1 The entire plunger assembly is urged outwardly by a coiled compression spring 305 interposed between the head of the bolt 304 and the inner end of the recess 390 to project the stem of the plunger into the' position shown in Fig. 8. An extension 300 of reduced diameter projecting rearwardly from the head of the bolt extends Movements of the cating with the inner end of the recess. A tapered plug 308 threaded into the hollow stem 302 acts to restrict the discharge opening for the air and thus regulates the rate at which the rearward movement of the plunger takes place The plug is provided with longitudinal grooves 309 to permit; the escape of air from the hollow stem. Upon movement of the work head to gauging position the plunger is projected outwardly while air enters the recess. through the passage above described. 1

The stop shaft 282 may be also utilized to advantage for actuating the revers ng switch RS which, as hereinbefore explained, controls the direction of rotation of the motor MI and therefore the direction of movement of the work carriage. Actuation of the switch iseifected by en gagement of the shaft alternately with a pair of reversing dogs 3"] and 3-H (Figs. 10, 10a and 12) adjustably mounted in spaced relation on a switch actuating bar 3I2. ported for e'ndwise sliding movement on the frame 262. above and slightly to the rear of the positioner bar. Such movements of the bar are transmitted to the switch RS through an arm 3 l 3 fast on the bar and an actuator 3H projecting horizontally from the switch casing. A yieldable connection 315 is provided between the arm and the actuator to compensate for the different range of movements of these parts. I

As shown in Fig. 10a, the reversing dog 3) s provided on its inner face with a pad 3I6 which 7 is normallyengageable by the stop' shaft as the work head moves into retracted position. This pad is arranged so that it can be moved out of the path of the stop shaft when it is desired to increase the range of 'movement of the work head since the head will then move sufficiently to bring the stop shaft into direct engagement with the dog 3"]. v To this end the pad is formed with a rearwardly projecting hub,3l1' 'journaled v in an aperture in the dog. The end portion of 1 3l2 and journaled on the frame 262.

the hub is formed with gear teeth 3! mes'iinrz with a gear 3i9 fast on a squared rod 320 extending generally parallel to the switch actuating bar Thus the pad can be swung to either its active or retracted positions by rocking the rod 320. A hand lrvcr '32I (Figs. 5 and 8) is fixed to the end of the ref. for rocking the same.

In setting up the machine for a particular class of work as for example, grinding internal screw threads previously rough machined in the work .piece W, the following initial adjustments or settings are made although not necessarily-in the order mentioned. It is assumed of course, that a-grinding wheel 23 of the proper grade and size has been mounted on the wheel head 24. If

necessitated by the length of the spindle, the wheel assembly is adjusted axially in the friction mounting sleeve 62so that the wheel is accurately located on the reference point P. The .wheel head is then s'wiveled to accurately aline the wheel with the helix angle of the threads to be ground. Corresponding adjustments are made in the set.-

The actuating bar is sup used for the narily wheel may then be roughly adjusted by means of the hand wheel 203 so that the dresser can operate to properly size and shape the wheel. These adjustments may be made with reference to a test work piece secured in place on the work spindlef In case the feed screw and nut assembly I90 previous job is unsuitable forthe work for whichthe machine'is being set up, this assembly is replaced by a suitable lead screw and nut assembly having a" pitch corresponding to the pitch of the threads to be ground. In installing'the new lead screw thespacers I93 may be appropriately arranged to located the screw member l9| so that the work piece may be retracted the desired distance from the grinding wheel. The range of feed movement is then determined by adjustment of the reversing dogs 31!) andf3ll on the switch actuating bar 3l2. 'Adjustment is' also made for right 'or left hand threadsas required by swinging the reversing gear bracket 182 into either its forward or reverse position.

With the machine thus set up the final sizing adjustment for depth of cut is made by :turning the stop shaft 282 until the stop button 28l engases the positioner bar 290 so as to locate the work exactly in position for the wheel tomake the finishing cut. The stop 291 is then set to Through the novel relationship of the grindin wheel and dressing apparatus, accurate sizing of the work is very readily attained. Moreover, any back lash developing in the feed mechanism through wear or the like may be effectually neutralized. In general it'is apparent that the invention provides a thread grinding machine particularly suitable for operation under production conditions and yet capable of finishing th work to a high degree'of precision.

I claim as my invention:

l. A thread grinding machine having, incombination, a rotatably driven grinding wheel, a carriage reciprocable toward and from'the grinding wheel, a feed shaft extending parallel to the reciprocatory path of the carriage, means for driv- I ing'said shaft-to impart feed and return movements to the carriages. work head mounted on said carriage for pivotal movement about the axis of said shaft, a work supportingspindle journaled on said head, a gear fixedtothe spindie, a gear fixed to'the shaft, a bracket mounted for pivotal'movement about the axis ofsaidshaft,

driving gear journaled in said bracketv and.

a meshing with the gear on said shaft, an idler gear journaled on the bracket and meshing with said driving gear, and means for swinging said bracket on its pivot to engage either'said driv-' ing gear or said idler gear selectively with the gear on said spindle. y

2. A thread grinding machine having, incombination, a rotatably driven'grinding. wheel, a. carriage'reciprocable toward and from the grinding wheel, a feed shaft extending parallel to the reciprocatory path, of the carriage, means for driving said shaft to impart feed and returnmove ments to the carriage, a'work head mounted on preventturning of the adjusting lever Ni -beyond 5 the set position.

In placing the machine inoperation the wheel driving motor M and work driving mottorMl are i started in the usual manner by manipulation of the push buttons on the switch panel-SP. Ordithe work will be given a series of passes relative to the wheel. Before the first pass is ,made, the stop shaft 282 is usually retracted to cause the wheel to make a. cut of minimum depth. Thereafter, for each pass, the stopshaft may be advanced a small amount to progressively increase the depth of out until the work is ground said carriage for pivotal movementabout the axis of said shaft,--a work supporting spindle journaled on said head, and means drivingly' connecting said shaft with said spindle, said connectingmeans being adjustable to cause the spin- I die to rotate either in the same direction as the shaft or in the opposite direction. g v 3. A thread grinding machine having, in combination, a rotatably driven grinding .wheel, a

carriage reciprocable toward and from the grinding wheel, a feed shaft extending parallel to the reciprocatory path of the carriage, means for to final size as indicated by the engagement of a the adjusting lever 29! with its cooperating stop 291] 7 After each pass of the work or 'afterseveral passes it may be desirable to gauge the work size.

This is done when the work carriage is in the Z retracted position, at which time the operator,

through the manual control lever 213; initiates the operation of the power mechanism for swing-.- ing the work head to its feed or gauging position. Manipulation of the control lever at any other time is rendered ineffective bythe safety locking mechanism actuated by the safety dog 2.14. This dogiof course, may be variably set as required for different classes of Work, I

' It will be apparent from the foregoing," that the invention provides a thread grinding machine of novel and improved construction particularly adapted for grinding internal threads with a'high degree of precision. The machine maybe readily set up for operating on a wide variety of work and all adjustments required during the actual operating cycle are quickly and easily made by means of controls conveniently accessibl at the front of the machine,

driving said shaft to impart feed and return movements to the carriage, a work head mounted on said carriage for pivotal movement about the axisof said shaft, a work supporting spindle journaledon said head, and driving means connecta "ing said shaft and said: spindle for rotatingthe spindle in timed relatlon to the-feed of the carriage. v

'4. A thread grinding machine having, in combination, a rotatably driven grinding wheel, means supporting work to be operated on' by said wheel comprising a carriage reciprocable toward and from the grinding wheel, a work head pivoted on said carriage-to swing transversely. .ofthe reciprocatory path of the carriage between an operatingposition in which the work is engageable by the grinding wheel and an inactive position in which the head isconvenientlyaccessible for loading and gauging the work; a powe'rdriven reciprocatory. member, a bell crank adapted to be rocked by said member in its reciprocation,

and alink connecting said bell crank with said head operative in the rocking of said bell crank to swing the head between its operating and loading positions; l v 5. In a machine of the class described, the

combination of a reoiprocable carriage, a feed shaft journaled on said carriage and reciprocable therewith, a lead screw keyed to the shaft, a stationary nut coacting with said lead screw, means for driving the shaft to impart feed and return movements to the carriage, said driving means including a driven shaft extending generally parallel to said feed shaft, pulleys nonrotatably secured to the respective shafts, an endless flexible driving member running over said pulleys and means for shifting the pulley on said drive shaft longitudinally thereof in synchronism with the movements of the carriage to maintain the pulleys in alinement.

6. In a thread grinding machine, in combination, a rotatably driven grinding wheel, a reciprocable work support, feed mechanism for advancing the work support to feed the work to the wheel, said feed mechanism including interengageable rotatable lead screw and relatively stationary nut members, power actuated means for driving said screw member, a control member movable to turn said nut for taking up the back lash in the feed mechanism, adjustable stops for limiting movement of said member to a predetermined. range, and a second control member normally movable with said first control member, but disengageable therefrom for independent movement, said second control member acting to rotate said nut to effect a predetermined adjustment of the work relative to the grinding wheel.

7. In a thread grinding machine, in combination, a rotatably driven grinding wheel, a reciprocable work support, feed mechanism for advancing the work support to-feed the work to the grinding wheel, said feed mechanism including interengageable rotatable lead screw and relatively stationary nut members, power actuated means-for driving said screw member, a control member operable to rotate said nut for effecting a predetermined adjustment of the work relative to the grinding wheel, a second control member operable to rotate said nut to take up back lash in the feed mechanism, and means for locking said control members together.

8. In a thread grinding machine, in combination, a rotatably driven grinding wheel, a reciprocable worksupport, feed mechanism for advancing the work support to feed the work to and from the grinding wheel, said feed mechanism-including interengageable rotatable lead screw and relatively stationary nut members, power actuated means for driving said screw member, control means for rotating said nut to effect a predetermined adjustment of the work and grinding wheel, other control means for rotating said nut to compensate for back lash in the feed mechanism, and adjustable stop means coacting with said last mentioned control means for limiting the degree of rotation imparted to sa d nut.

9. A thread grinding machine having, in combination, a rotatably driven grinding wheel, a work supporting carriage, feed mechanism for advancing the carriage to feed the work to the grinding wheel, said mechanism including a power driven shaft, a stationariiy supported nut, a lead screw keyed to said shaft and engageable with said nut, and aseries of spacers on said shaft for holding the lead screw against movement axialfy of the shaft, said spacers being interchangeable to accommodate lead screws of different lengths.

10. A thread grinding machine having, incombination, a rotatably driven grinding wheel, a

work supporting carriage, feed mechanism for advancing the carriage to-feed the work to the grinding wheel, said mechanism including a power driven shaft, a stationarily supported nut, a tubular member keyed to said shaft having lead screw threads engageable with said nut, and means adjustable to variably position said member axially of the shaft to variably locate the work with respect to the grinding wheel.

11. In a grinding machine, in combination, a base, a work slide reciprocably mounted thereon, means on said slide for rotatably supporting a work piece for movement therewith in a direction axial of the work piece, a primary slide mounted for movement transversely of said work slide, a wheel slide mounted on said primary slide for movement transversely of the work slide, a dresser slide mounted,on said primary slide at one side of said wheel slide formovement in a path generally parallel to the path of the wheel slide, stop means for determining the limitposition of the dresser slide, control means operthreads, in combination, a base, a work slide re ciprocably mounted thereon, means for rotate ably supporting a work piece on said slide for axial traverse therewith, a primary slide sup-' ported for reciprocation transversely of said work slide, a secondary slide supported on said primary slide for movement therewith and for independent movement relative thereto, a rotatably driven grinding wheel mounted on said secondary slide, feed mechanism for advancing the work slide to feed the work piece to the grinding wheel at a predetermined rate, control means operable to position said secondary slide for determining the depth of cut taken by the grinding wheel, and means operable by said work slide in its feed movement for shifting. said primary and secondary slides together to determine the taper to be ground on the work piece.

13. In a thread grinding machine having a, roe tatably driven grinding wheel, a combination of a support for work to be operated on by the wheel, feed mechanism for efiecting relative re- 7 ciprocation between the work support and the grinding wheel, said mechanism including lnterengaging lead screw and nut members, power actuated means for driving said lead screw, a rotatable frame supporting said nut, a first control member manually operable to rotate said frame and thereby effect a predetermined adjustment of the work and the grinding wheel, a second control member adapted to be disengageably latched to said first control member, and means carried by said second control member for limiting the rotational movement of said frame to a range effective to take up back lash in the feed mechanism.

14. A thread grinding machine having, in combination, a base, relatively shiftablework and grinding wheel supports on said base, a feed shaft associated with one of said supports and shiftable therewith, means for driving said feed shaft including a power driven shaft journaled on the base and extending generally parallel to said feed shaft, a member drivingly coupled with the 

